Protein structures represent a compromise between static order and dynamics; a certain amount of rigidity is required to maintain the high specificity exhibited by enzymatic reactions, while flexibility of the polypeptide chain is needed for substrate binding and product release. In this program grant, all projects use the absorption of a visible or infrared photon to electronically or vibrationally excite a biomolecule. Relaxation events will be followed on the time scale of fsec to msec using specialized techniques that allow for resolution at the atomic and molecular level. High resolution spectroscopy of porphyrin in hemoproteins, carried out by Vanderkooi, reveals vibrational features of ground and excited state molecules and allow for the examination of the question whether all protein molecules have identical reactivity. Dutton will be using bacterial reactions centers to photoinitiate reduction of coenzyme Q and examine by infrared spectroscopy which amino acids participate in the reaction. Hochstrasser, making use of ultra fast infrared techniques developed in his laboratory, will be examining relaxation processes in photosynthetic reaction centers and model systems. Therien, who brings expert synthetic skills to the program project, will be using heme and coenzyme Q models to study the role of particular vibrational modes in electron transfer reactions. Yonetani will examine the role of amino acid composition of the heme pocket on metal ligation processes of hemoproteins using magnetic resonance, optical and infrared spectroscopy.